Baltimore, Annapolis and/or DC area campsites

It really depends on how much time will be spent where. If Baltimore & Annapolis are the primary attractions then the Millersville KOA is the one. For DC I'd be inclined to move to a CG closer to DC. Cherry Hill is hellishly expensive for the questionable convenience of having a bus to the METRO.

I'll add Lake Fairfax Countty Park to Bull Run & Green Belt for CGs much cheaper than CH but close enough to a METRO staion with relatively inexpensive all day parking. LFCP is an oasis of tranquility, besides maybe Dulles air traffic by day, compared to CGs close to major highways.